Process for forming electrodes for semiconductor devices by focused ion beam technology

ABSTRACT

A process for forming electrodes for semiconductor devices having a semiconductor substrate and an electrically conductive portion covered and protected by an electrically insulating coating. The process includes the steps of forming an electrically conductive film on the electrically insulating coating, forming an electrode to be connected to an external circuit on the electrically conductive film at a position overlying the electrically conductive portion by exposing portions of the electrically insulating coating and the first electrically conductive film to a converged ion beam, electrically connecting the electrode to the exposed portions of the electrically conductive film, and removing the portions of the electrically conductive film not covered by the electrode. As a result, the likelihood of breakdown of the internal circuit of the semiconductor device connected to the electrically conductive portion while the electrode is being formed is greatly reduced.

This application is a division of application Ser. No. 07/118,031 filedNov. 9, 1987, U.S. Pat. No. 4,853,341.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for forming electrodes forsemiconductor devices, and more particularly to a process for forming anelectrode for providing an electrical connection between an externalcircuit and an electrically conductive portion of the semiconductordevice such as a metal wiring layer protectively covered by anelectrically insulating coating.

2. Description of the Prior Art

When a semiconductor device having its surface covered by anelectrically insulating coating is subjected to failure analysis, ananalyzing electrode electrically connected to the internal circuit ofthe semiconductor device must frequently be newly formed on theelectrically insulating protective coating. A semiconductor device to beanalyzed may not have been provided with external lead terminals orbonding pads, or even if the semiconductor device has external leadterminals or bonding pads, it may be difficult to obtain a satisfactoryfailure analysis merely by utilizing the incoming/outgoing signalspassing through the external lead terminals or the bonding pads. Inthese cases, if electrical signals are to be transmitted to and receivedfrom the internal circuit of the semiconductor device, it becomesparticularly necessary to form such an analyzing electrode.

When an electrically conductive portion such as metal wiringconstituting a part of the semiconductor device has a large pattern sizeor the interval between two adjacent patterns is large, the metal wiringmay be exposed by partially or completely removing the electricallyinsulating protective coating of the semiconductor device. Subsequently,if a probe is directly brought into contact with the thus-exposed metalwiring, electrical signals can be transmitted to and received from theinternal circuit of the semiconductor device for analyzing purposes.

Recently, however, as semiconductor devices have become increasinglyintegrated and more complicated, the pattern size of their metal wiringand the interval between adjacent patterns have been reduced to asignificant extent. Therefore, such a size or interval is far smallerthan the tip diameter of the probe, and this may cause variousdifficulties; for example, the tip of the probe may cause damage to themetal wiring during failure analysis. This makes it difficult to subjectsemiconductor devices to failure analysis. To cope with this problem,the following prior-art process has been utilized. In the conventionalprocess which will be described later, an analyzing electrode having asize larger than the tip diameter of the probe is formed on theelectrically insulating protective coating of a semiconductor device,with the analyzing electrode electrically connected to the internalcircuit of the device. In order to transmit and receive electricalsignals to and from the internal circuit of the device, a probe isbrought into contact with the thus-formed analyzing electrode.

FIGS. 5A to 5E are respectively diagrammatic, cross sections used forexplaining a process sequence for forming an electrode for asemiconductor device according to the prior art. The prior-art processfor forming an electrode will be described below with reference to FIGS.5A to 5E.

Referring first to FIG. 5A, a semiconductor substrate of oneconductivity type is indicated at 110, and includes a source (or drain)121 and a drain (or source) 122 both of which are formed asimpurity-diffused regions. P-n junctions 131 and 132 are respectivelyformed at the boundary between the source (or drain) 121 and thesubstrate 110 as well as that between the drain (or source) 122 and thesubstrate 110. The substrate 110 partially serves as a channel regionfor providing an electrical connection between the source (or drain) 121and the drain (or source) 122. A gate oxide film 123 is formed on theportion of the substrate 110 that forms such a channel region, and agate electrode 124 is further formed on the film 123, therebyconstituting a MOS transistor 120. Metal wires 1 each serving as anelectrically conductive portion are respectively connected to the gateelectrode 124, the source (or drain) 121 and the drain (or source) 122.An isolation film 140 electrically isolates the metal wires 1 from thesubstrate 110 as well as the metal wires 1 from one another. The entiresurface of the semiconductor device having the aforesaid arrangement iscovered by an electrically insulating protective coating 2 serving as anisolation layer so that the device surface may be smoothed and at thesame time the semiconductor device may be protected from contamination.

As shown in FIG. 5A, in order to dispose an analyzing electrode on thethus-formed semiconductor device, a converged ion beam 3 is locallyirradiated onto the portion of the electrically insulating protectivecoating 2 overlying a connecting portion 11 of the metal wire 1 to whichthe analyzing electrode is to be connected.

Referring to FIG. 5B, the constituent atoms of the thus-irradiatedportion of the electrically insulating protective coating 2 arescattered by the phenomenon of sputtering through irradiation of theconverged ion beam 3, and to thus bore into the irradiated portion.

As shown in FIG. 5C, this boring is continued until the desired portionof the metal wire 1 is exposed, that is, to a depth required forelectrical connection. Thus, a predetermined opening is formed in theelectrically insulating protective coating 2.

Referring to FIG. 5D, while a gaseous or vaporized metal compound 31,which can be decomposed to generate a metal through irradiation of aconverged ion beam, is being supplied to an area which includes aportion to be bored, i.e., the connecting portion 11 and whichcorresponds to the shape and size of an analyzing electrode to beformed, this area is also being irradiated with the converged ion beam 3to cause decomposition of the metal compound 31, thereby forming a film6.

After the film 6 having a predetermined shape, size and thickness hasbeen formed, the irradiation of the converged ion beam 3 and the supplyof the metal compound 31 are stopped. As shown in FIG. 5E, the metalfilm 6 obtained in this final step serves as an analyzing electrode 4.

However, the aforesaid prior-art process for forming an analyzingelectrode involves the following disadvantages which will be describedbelow with reference to FIGS. 6A to 6C.

FIG. 6A is a diagrammatic, cross section used for explaining thedisadvantages of the prior-art process for forming an analyzingelectrode for a semiconductor device.

Referring to FIG. 6A, Cm represents the electrical capacitance which isproduced between the substrate 110 and the metal wire 1 to which theanalyzing electrode 4 is to be connected, that is before the electrode 4has been formed. Ce represents the electrical capacitance which isproduced between the substrate 110 and the analyzing electrode 4including the metal wire 1 to which the electrode 4 is finallyconnected, that is after the electrode 4 has been formed on the metalwire 1. Ib represents the ion current of the converged ion beam 3. Terepresents the ion irradiation period which is required to form theanalyzing electrode 4 on the protective coating 2 by irradiating themetal film 6 with the converged ion beam 3 while the metal compound 31is being supplied. Ve represents the potential difference between thesubstrate 110 and the analyzing electrode 4 including the metal wire 1.Vt represents the critical potential difference Ve which causesbreakdown of the semiconductor device, that is, the value of withstandvoltage. Also, secondary electrons generated through irradiation of theconverged ion beam 3 are indicated by 32.

After the electrically insulating protective coating 2 has been boreduntil the desired portion of the metal wire 1 is exposed, the metalcompound 31 is decomposed through irradiation of the converged ion beam3. The analyzing electrode 4 is formed by growing the thus-generatedmetal film 6 in an area which corresponds to the predetermined shape andsize of the analyzing electrode 4 and which includes the bored portion,i.e., the connecting portion 11. In the meantime, the ion current Ib ofthe converged ion beam 3 is incident upon the metal wire 1. The flow ofthe ion current Ib upon the metal wire 1 continues until the metal film6 reaches a predetermined shape, size and thickness to form theanalyzing electrode 4. Accordingly, after the ion irradiation period Tehas elapsed, that is, when the formation of the analyzing electrode 4 iscomplete, the quantity of electric charge Qe supplied to the metal wire1 becomes Qe=Ib.Te, and the potential difference Ve between the metalwire 1 and the substrate 110 becomes Ve=Qe/Ce. Therefore, even if theion current Ib, the ion irradiation period Te of the converged ion beam3 and the quantity of electric charge Qe are respectively the same, asthe electrical capacitance Ce becomes smaller, the potential differenceVe becomes larger.

However, in highly integrated semiconductor devices, the electricalcapacitance Cm is relatively small because of the extremely reducedpattern sizes of, for example, the MOS transistor 120, the source (ordrain) 121, the drain (or source) 122, the gate electrode 124, the metalwires 1 and other constituent elements. Also, since the gate oxide film123 is extremely reduced in thickness, the withstand voltage Vt of thegate oxide film 123 is of a low level. Since the interval between thesubstrate 110 and the analyzing electrode 4 is greater than thethickness of the gate oxide film 123, the electrical capacitance betweenthe substrate 110 and the electrode 4 is relatively small and theelectrical capacitance Ce including the aforesaid capacitance Cm is alsorelatively small. In the case of such small electrical capacitance Ce,if the quantity of electric charge Qe based on ordinary levels of Ib andTe is supplied to the metal wire 1, the potential difference Ve readilyexceeds the level of the withstand voltage Vt. This may result in thebreakdown of the semiconductor device.

As an example, if the analyzing electrode 4 having a size which allowsthe tip of an ordinary type of probe to be brought into contact with theelectrode 4, for example, a square form with each side 80 to 120 umlong, is to be formed in accordance with the aforesaid process, almostall semiconductor devices will be broken before an analyzing electrodewith such a size can be formed.

In such cases, in order to prevent the occurrence of breakdown in thesemiconductor devices, the size of the analyzing electrode 4 may beenlarged to increase the value of Ce. However, if the size is enlarged,the ion irradiation period Te is extended to increase the values of Qeand Ve, thereby causing the level of Ve to exceed that of Vt. This mayalso result in the breakdown of the semiconductor device.

In particular, since the converged ion beam 3 is commonly a beam ofpositive ions, a secondary ion current Ise of the secondary electrons 32produced through irradiation of the converged ion beam 3 flows in thesame direction as that of the ion current Ib. Therefore, the potentialdifference Ve becomes Ve=(Ib+Ise).Te/Ce, and exceeds thepreviously-mentioned level of Ve. In consequence, it becomes even easierfor the semiconductor device to breakdown.

More specifically, referring to another example shown in FIG. 6B, whilethe converged ion beam 3 is being irradiated until the metal film 6having a predetermined shape, size and thickness is obtained, thepotential at the gate electrode 124 which is electrically connected tothe metal wire 1 and the metal film 6 exceeds the level of withstandvoltage of the gate oxide film 124 to cause dielectric breakdown of thegate oxide film 124. This results in the failure of the MOS transistor120.

Referring to the other example shown in FIG. 6C, the potential at thesource (or drain) 121 electrically connected to the metal wire 1 exceedsthe level of withstand voltage of the p-n junction to cause breakdown ofthe p-n junction 131, and thus results in the failure of the MOStransistor 120.

As described above, use of the prior-art process for forming anelectrode easily causes breakdown of a semiconductor device to beanalyzed, and this may lead to the problem that correct failure analysiscan not be performed.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a processfor forming an electrode for a semiconductor device in which it ispossible to positively form an electrode over a desired area on thesemiconductor device without involving the risk of causing breakdown ofthe device.

In accordance with the present invention, an electrically conductivefilm or layer is formed over an electrically insulating film overlyingthe surface of a semiconductor substrate prior to the formation of anelectrode which is to be connected to an external circuit and, followingthe formation of the electrode, the portion of the electricallyconductive film or layer which is not covered by the electrode isremoved. Therefore, since the electrical capacitance of the thus-formedelectrode increases positively, the degree of increase in the potentialdifference between the electrically conductive portion and thesemiconductor substrate is reduced with respect to the level of thewithstand voltage of the semiconductor device. This greatly reduces thelikelihood that the internal circuit of the semiconductor deviceconnected to the electrically conductive portion will be broken.Accordingly, the present invention enables exact failure analysis ofsemiconductor devices.

Further objects, features and advantages of the present invention willbecome apparent from the following description of preferred embodimentsof the present invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1G are diagrammatic, cross sections used for explaining aprocess sequence which is carried out by a process constituting a firstpreferred embodiment of the present invention;

FIGS. 2A to 2I are diagrammatic, cross sections used for explaining aprocess sequence constituting a second preferred embodiment of thepresent invention;

FIGS. 3A to 3J are diagrammatic, cross sections, used for explaining aprocess sequence constituting a third preferred embodiment of thepresent invention;

FIGS. 4A to 4K are diagrammatic, cross sections used for explaining aprocess sequence constituting a fourth preferred embodiment of thepresent invention;

FIGS. 5A to 5E are diagrammatic, cross sections used for explaining aprocess sequence for an electrode forming process relying upon the priorart; and

FIGS. 6A to 6C are diagrammatic, cross sections used for explaining thedisadvantages of an electrode forming process which relies upon theprior art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A process for forming an electrode for a semiconductor device inaccordance with the present invention will be described below withreference to the accompanying drawings in which like reference numeralsare used to denote like or corresponding elements relative to those inpreferred embodiments which will be mentioned later.

FIGS. 1A to 1G show each step of the process sequence constituting afirst preferred embodiment of the invention.

Referring to FIG. 1A, the semiconductor device 100 has the samearrangement as that of the semiconductor device previously mentioned inthe description of the prior-art. More specifically, the semiconductordevice includes a semiconductor substrate 110 a source (or drain) 121and a drain (or source) 122 both of which are formed asimpurity-diffused regions. The p-n junctions 131 and 132 arerespectively formed at the boundary between the source (or drain) 121and the substrate 110 as well as that between the drain (or source) 122and the substrate 110. The substrate 110 partially serves as a channelregion for providing electrical connection between the source (or drain)121 and the drain (or source) 122. The gate oxide film 123 is formed onthe portion of the substrate 110 that forms such a channel region, andthe gate electrode 124 is further formed on the film 123, therebyconstituting the MOS transistor 120. The metal wires 1 each serving asan electrically conductive portion are respectively connected to thegate electrode 124, the source (or drain) 121 and the drain (or source)122. The isolation film 140 electrically isolates the metal wires 1 fromthe substrate 110 as well as the metal wires 1 from one another. Theentire surface of the semiconductor device having the aforesaidarrangement is covered by the electrically insulating protective coating2 so that the device surface may be smoothed and at the same time thesemiconductor device may be protected from contamination.

As shown in FIG. 1B, a first electrically conductive first metal film 5is deposited on the electrically insulating protective coating 2overlying the semiconductor device. This coating is effected over a widearea including the portion of the coating 2 overlying the connectingportion 11 of the metal wire 1 which is to be electrically connected tothe analyzing electrode 4 for external connection. It is preferred thatthe first metal film 5 be deposited without causing electrical breakdownof the semiconductor device in this coating step. Therefore, forexample, a 10-nm-thick gold (Au) film may preferably be coated over theelectrically insulating protective coating 2 of the semiconductor deviceby using known vapor deposition or sputtering methods that involve noelectrical charging or low level of electrical charging.

Subsequently, as shown in FIG. 1C, the converged ion beam 3 isirradiated onto a desired portion of the first metal film 5 overlyingthe protective coating 2 at a desired position in correspondence withthe connecting portion 11 to which the analyzing electrode 4 is to beconnected. The constituent atoms of the thus-irradiated portions of thefirst metal film 5 and the protective coating 2 are scattered bysputtering to thus bore into the first metal film 5 and the protectivecoating 2. The converged ion beam 3 may, for example, be a gallium ion(Ga⁺) beam having 30-KeV ion beam energy with an ion beam current of 400to 100 pA. Use of such a converged ion beam 3 enables boring of theelectrically insulating protective coating 2 which is made, for example,of a silicon oxide (SiO₂) film, a silicon nitride (Si₃ N₄) film, a filmof phosphosilicate glass (PSG) or multi-layers thereof. This boring iscontinued until the portion of the metal wire 1 corresponding to theconnecting portion 11 is exposed, that is, until a depth required forelectrical connection is reached. Subsequently, the irradiation of theconverged ion beam 3 is stopped, and the boring of the electricallyinsulating protective coating 2 is completed. The state of thethus-bored protective coating 2 is illustrated in FIG. 1D.

Referring to FIG. 1E, while a gaseous or vaporized metal compound 31,which can be decomposed to generate metal through irradiation of an ionbeam, is being supplied to an area which includes the bored portion orthe connecting portion 11 and which corresponds to the shape and size ofthe analyzing electrode 4 to be formed, this area is also beingirradiated with the converged ion beam 3 to cause decomposition of themetal compound 31, thereby forming a second metal film 6 which providesa analyzing electrode 4 to be connected to an external circuit.

After the metal film 6 having a predetermined shape, size and thicknesshas been formed, the irradiation of the converged ion beam 3 and thesupply of the metal compound 31 are stopped. The metal compound 31 ismade of, for example, tungsten carbonyl (Mo(CO)₆). If a metal compound31 made of tungsten carbonate is with the converged ion beam 3 includinggallium ions (Ga⁺) having 30-KeV ion beam energy with an ion beamcurrent of 400 to 100 pA, a 100-nm-thick film of tungsten (W) can beformed as the analyzing electrode 4. In this case, if the metal compound31 is made of molybdenum carbonyl (Mo(CO)₆), a film of molybdenum isproduced as the analyzing electrode 4. FIG. 1F illustrates the statewherein the just-described step is completed.

Finally, the portion of the first metal film 5 which is not covered bythe analyzing electrode 4 provided by the second metal film 6 is removedby using known means of removing the first metal film 5. The known meansis of the type that erodes the first metal film or electricallyconductive film 5 but does not erode the electrically insulatingprotective coating 2 or the second metal film or the connectingelectrode 6 used for external connection. The aforesaid means ofremoving the first metal film 5 from the the electrically insulatingprotective coating 2 except for the area which is covered by the secondmetal film 6 is, for example, a known form of plasma etching techniquewhich employs an etching gas including carbon tetrafluoride (CF₄) mixedwith oxygen (O₂). Use of such a known removing means makes it easy toetch away the first metal film 5 only, but the portion of the firstmetal film 5 covered by the second metal film 6 does not suffercorrosion. Specifically, the first metal film 5 underlying the secondmetal film 6 does not suffer any serious side etching, and this preventsthe occurrence of peeling of the second metal film 6.

The second metal film 6 which has been obtained through theabove-described process serves as the analyzing electrode 4, as shown inFIG. 1G.

In the aforesaid process sequence for forming the analyzing electrode 4,the area occupied by the first metal film 5 is larger than that occupiedby the second metal film 6. The first metal film 5 underlies the secondmetal film 6, and both of them are electrically connected to each other.If Ca represents the electrical capacitance which is produced betweenthe substrate 110 and the first and second metal films 5 and 6 includingthe metal wire 1, it will be readily understood from the size of thearea occupied by the first metal film 5 that the value of Ca is greaterthan that of the electrical capacitance Ce explained previously in thedescription of the prior art with reference to FIG. 6A. Accordingly,even if Ib, Ise, Te and the quantity of electric charge Q are the sameas those used in the prior-art process explained with reference to FIG.5D, the potential difference Va (Va=Qe/Ca=Ib.Te/Ca; when considering theinfluence of the secondary electrons 32, Va=(Ib+Ise).Te/Ca) which isproduced when the second metal film 6 overlies the first metal film 5,the electrical capacitance Ca is smaller than the potential differenceVe (Ve=Qe/Ce=Ib.Te/Ce; when considering the influence of the secondaryelectrons 32, Ve=(Ib+Ise).Te/Ce) which is associated with the electricalcapacitance Ce produced in the prior-art process. Accordingly, even ifdecomposition of the metal compound 31 is continued through irradiationof the converged ion beam 3 until the analyzing electrode 4 having apredetermined shape and size is formed on the second metal film 5, thedegree of increase in the potential difference between the semiconductorsubstrate 110 and the first and second metal films 5 and 6 including themetal wire 1 is reduced as compared with that experienced with the priorart. Accordingly, the level of the aforesaid voltage difference Vaseldom exceeds that of the withstand voltage Vt, thereby significantlyreducing the frequency of the occurrence of breakdown of a semiconductordevice to be analyzed. In addition, if the first metal film 5 is coatedon the widest possible surface area of the electrically insulatingprotective coating 2, for example, if the film 5 is coated on the entiresurface of a semiconductor device which assumes a chip or wafer form, itis possible to completely prevent the breakdown of the semiconductordevice during the process sequence for forming the second metal film 6or the analyzing electrode 4 on the same.

It is to be noted that, since the converged ion beam 3 having a beamdiameter of 0.3 μm can be easily obtained by using gallium ions (Ga⁺)mentioned in the aforesaid embodiment, it is possible to easily providean electrical connection to the very thin metal wire 1 incorporated inthe latest highly integrated type of semiconductor device. Also, sincethe converged ion beam 3 can be easily deflected and scanned, the ionbeam 3 can be scanned within a predetermined area to form the analyzingelectrode 4 having desired shape and size.

In the aforesaid embodiment, although the connecting portion 11 isformed on the metal wire 1, the connecting portion 11 may be formed on asingle-cystal silicon (Si) substrate or a single-crystal orpolycrystalline silicon (Si) film to deposit the analyzing electrode 4thereon.

FIGS. 2A to 2I are diagrammatic, cross sections used for explaining aprocess sequence constituting a second preferred embodiment of thepresent invention.

It is to be noted that, since FIGS. 2A and 2B are views similar to thepreviously-described FIGS. 1A and 1B and illustrate the same steps, thedetailed description will be omitted.

As shown in FIG. 2C, the metal compound 31 is supplied to a desired areaof the first metal film 5 overlying the connecting portion 11 to beformed and at the same time the converged ion beam 3 is irradiated ontothe area of the first metal film 5 which corresponds to the shape andsize of the analyzing electrode 4 to be formed, thereby forming thesecond metal film 6. After the second metal film 6 having predeterminedshape, size and thickness has been formed, the irradiation of theconverged ion beam 3 and the supply of the metal compound 31 arestopped. FIG. 2D illustrates the state in which the just-described stepis completed.

Subsequently, as shown in FIG. 2E, the second metal film 6, the firstmetal film 5 and the electrically insulating protective coating 2 arebored through irradiation of the converged ion beam 3. This boring iscontinued until the portion of the metal wire 1 corresponding to theconnecting portion 11 is exposed, that is, a depth required forelectrical connection is reached. Subsequently, the irradiation of theconverged ion beam 3 is stopped, and the boring of the electricallyinsulating protective coating 2 is completed. FIG. 2F illustrates thestate of the protective coating 2 which is thus bored throughirradiation of the converged ion beam 3.

Subsequently, as shown in FIG. 2G, while the metal compound 31 is beingsupplied, the desired area including the bored portion is irradiatedwith the converged ion beam 3, thereby forming embedded metal or anelectrically conductive film 61. Following the formation of the embeddedmetal 61 having predetermined shape, size and thickness which canprovide an electrical connection between the metal wire 1 and the secondmetal film 6, the irradiation of the converged ion beam 3 and the supplyof the metal compound 31 are stopped. FIG. 2H shows the state in whichthe just-described step is completed.

Finally, the portion of the first metal film 5 which is not covered bythe second metal film 6 and the embedded metal 61 is removed by usingknown means of removing the first metal film 5 only. The known means isof the type that erodes the first metal film 5 but does not erode theelectrically insulating protective coating 2, the second metal film 6 orthe embedded metal 61.

The second metal film 6 and the embedded metal 61 which have beenobtained through the above-described process sequence constitute theanalyzing electrode 4 as shown in FIG. 2I.

In the aforesaid second embodiment, after the metal wire 1 has beenexposed at the connecting portion 11, the metal compound 31 isdecomposed to generate the embedded metal 61 through irradiation of theconverged ion beam 3. However, the ion irradiation period in thisembodiment is shorter than the ion irradiation period required in thepreviously described first embodiment. Accordingly, the likelihood ofbreakdown of semiconductor devices is further reduced as compared withthat of the first embodiment.

FIGS. 3A to 3I are diagrammatic, cross sections used for explaining aprocess sequence constituting a third preferred embodiment of thepresent invention, with FIG. 3I being a perspective view of FIG. 3H.

The third embodiment will be described below, with the semiconductordevice shown in FIG. 3A having the same arrangement as that of thesemiconductor device of FIG. 1A referred to in the first embodiment.

In the third embodiment, as shown in FIG. 3B, the converged ion beam 3is irradiated onto the electrically insulating protective coating 2 ofthe semiconductor device 100, thereby forming a first metal film 105which serves as a line-shaped or band-shaped electrically conductivelayer which extends from a portion 7 to a predetermined area of thecoating 2 including a portion overlying the connecting portion 11 of themetal wire 1 which is to be electrically connected to the analyzingelectrode 4. The portion 7 is at the same potential as that of thesubstrate 110 and is hereinafter referred to as a "substrate potentialportion". More specifically, while the gaseous or vaporized metalcompound 31 which is decomposed to generate metal through irradiation ofthe converged ion beam 3 is being supplied, the converged ion beam 3 isscanned over the line-shaped or band-shaped area to form the first metalfilm 105 having a line-shaped or band-shaped form. However, the shape ofthe first metal film 105 is not confined to the line-shaped orband-shaped form; for example, it may be formed in a planar shape.

When a converged ion beam 3 is used, it is possible to form a very finepattern on the submicron order. Since this pattern formation isperformed through maskless deposition, direct lithography is possibleunder computerized control. In addition, there is an advantage in thatthis process as a whole is a low-temperature process which needs noheating step.

The metal compound 31 is made of, for example, tungsten carbonyl (W(CO₆)as in the case of the aforesaid first embodiment. If such a metalcompound 31 is combined with the converged ion beam 3 including galliumions (Ga⁺) having 30-KeV ion beam energy with an ion beam current of 100pA to 2 nA, it is possible to form a tungsten (W) film as the firstmetal film 105 having, for example, a thickness of 100 nm and a width of300 nm which realize in combination the effect of the process of theinvention. The first metal film 105 having such thickness and width haselectrical conductivity of the level required for performance of theeffect of the invention. The metal compound 31 may be made of molybdenumcarbonyl (Mo(CO)₆), and, in this case, a molybenum (Mo) film is producedas the first metal film 105.

Also, the first metal film 105 may be coated, for example, by usingknown vapor deposition or sputtering of the type that involves noelectrical charging or a low level of electrical charging, withoutcausing electrical breakdown of the semiconductor device in this coatingstep as in the case of the above-described first preferred embodiment.

Subsequently, as shown in FIG. 3C, the converged ion beam 3 isirradiated onto the desired portion of the first metal film 105overlying the protective coating 2 in correspondence with the connectingportion 11 to which the analyzing electrode 4 is to be connected. Theconstituent atoms of the thus-irradiated portions of the first metalfilm 105 and the protective coating 2 are scattered by sputtering. Thus,the first metal film 105 and the protective coating 2 are bored. As theconverged ion beam 3, a gallium ion (Ga⁺) beam having 30-KeV ion beamenergy with an ion beam current of 400 to 100 pA, for example, may beused. Use of such a converged ion beam 3 enables boring of theelectrically insulating protective coating 2 which is composed, forexample, of a silicon oxide (SiO₂) film, a silicon nitride (Si₃ N₄)film, a film of phosphosilicate glass (PSG) or multi-layers thereof.This boring is continued until the portion of the metal wire 1corresponding to the connecting portion 11 is exposed, that is, until adepth required for electrical connection is reached. Subsequently, theirradiation of the converged ion beam 3 is stopped, and the boring ofthe electrically insulating protective coating 2 is completed. FIG. 3Dillustrates the bored state obtained through the irradiation of theconverged ion beam 3.

Referring to FIG. 3E, while the gaseous or vaporized metal compound 31decomposed to generate metal through irradiation of the converged ionbeam 3 is being supplied to an area which includes the bored portion orthe connecting portion 11 and which corresponds to the shape and size ofthe analyzing electrode 4 to be formed, this area is irradiated with theconverged ion beam 3 to cause decomposition of the metal compound 31,thereby forming the second metal film 6. After the metal film 6 having apredetermined shape, size and thickness has been formed, the irradiationof the converged ion beam 3 and the supply of the metal compound 31 arestopped. The metal compound 31 is made of, for example, tungstencarbonyl (W(CO)₆). If such an illustrative metal compound 31 is combinedwith the converged ion beam 3 including gallium ions (Ga⁺) having 30-KeVion beam energy with an ion beam current of 100 pA to 2 nA, a100-nm-thick film of tungsten (W) can be formed as the second metal film6 to serve as the analyzing electrode 4 having a sufficient thickness.If the metal compound 31 is made of molybdenum carbonate carbonyl(Mo(CO)₆), a molybenum (Mo) film is produced as the second metal film 6.In this case, it is possible to use metal compounds of any type thatproduce metal by being decomposed through irradiation of the convergedion beam 3. FIG. 3F illustrates the final state wherein thejust-described step is completed. The decomposition of the second metalfilm 6 in the just-described step, that is, the step of forming theanalyzing electrode 4 proceeds in a state wherein the substratepotential portion 7 is electrically connected to the second metalcoating 6. Therefore, the semiconductor device 100 is never broken.

Finally, the entire process is completed by disconnecting the electricalconnection between the thus-formed analyzing electrode 4 and thesubstrate potential portion 7. As shown in FIG. 3G, such disconnectionmay be effected by disconnecting a given portion of the electricallyconductive layer or the first metal film 105 which is not covered by theanalyzing electrode 4. Alternatively, such disconnection may be effectedthrough irradiation of energy rays other than the converged ion beam 3,for example, a laser beam. Furthermore, the aforesaid electricalconnection may be disconnected by eroding the first metal film 105through chemical etching or plasma etching. FIGS. 3H and 3I respectivelyshow, in cross section and perspective, the semiconductor device 100having the thus-formed analyzing electrode 4.

In order to disconnect the electrical connection between the analyzingelectrode 4 and the substrate potential portion 7, as shown in FIG. 3J,the portion of the first metal film 105 which is not covered by thesecond metal film 6 may be removed by removal means of the type whicherode the first metal film 105 but do not erode the electricallyinsulating protective coating 2 or the second metal film 6. Such removalmeans may preferably be selected from the group consisting of chemicaletching or plasma etching employing etching gas under the conditionsthat the first metal film 105 is rapidly etched while the electricallyinsulating protective coating 2 and the second metal film 6 are slowlyetched. In this case, if the first metal film 105 and the second metalfilm 6 are made of a similar metal material, since the area in which theanalyzing electrode 4 is to be formed is constituted by both the firstmetal film 105 and the second metal film 6, if the etching conditionssuch as etching time are suitably selected, it is possible to removeonly the portion of the first metal film 105 which is not covered by thesecond metal film 6 with the second metal film 6 left in place. In thiscase, even if the thickness of the area serving as the analyzingelectrode 4 is somewhat reduced, failure analysis is not precluded inpractical terms. In the case of the illustratively-described arrangementincluding: the electrically insulating protective coating 2; the firstmetal film 105 and the second metal film 6, an etching gas may be, forexample, a mixed gas containing carbon tetrafluoride (CF₄) and oxygen(O₂).

In this manner, the portion of the first metal film 105 which is notcovered by the second metal film 6 is completely removed, none of thefirst metal film 105 will remain except for those regions in which theanalyzing electrode 4 is to be formed. Therefore when a plurality ofanalyzing electrodes 4 are to be formed on the semiconductor device 100,the just-described process is recommended.

In the above-described third embodiment, the substrate potential portion7 is provided on the portion of the metal wire 1 which is formeddirectly on the substrate 110 and which is at the same potential as thatof the substrate 110. However, a portion of the substrate 110 may beutilized as the substrate potential portion 7.

Also, as described previously with reference to FIGS. 3C and 3D, theconstituent atoms of the electrically insulating protective coating 2are scattered through irradiation of the converged ion beam 3. Thus, theelectrically insulating protective coating 2 is bored until the surfaceof the substrate 110 is exposed, and the thus-bored portion may beutilized as the substrate potential portion 7.

FIGS. 4A to 4K are diagrammatic, cross sections used for explaining aprocess sequence of a fourth preferred embodiment for forming anelectrode for a semiconductor device in accordance with the presentinvention.

FIGS. 4A and 4B are views similar to FIGS. 3A and 3B, respectively, andthe descriptions thereof will be omitted.

Referring to FIG. 4C, the metal compound 31 is supplied to the desiredarea of the first metal film 105 which includes a portion correspondingto the connecting portion 11 to which the electrode 4 is to be connectedand at the same time the converged ion beam 3 is irradiated onto thearea of the first metal film 105 which corresponds to the shape and sizeof the analyzing electrode 4 to be formed. In this manner, the metalcompound 31 is decomposed to generate metal through irradiation of theconverged ion beam 3, thereby forming the second metal film 6. After thesecond metal film 6 having a predetermined shape, size and thickness hasbeen formed, the irradiation of the converged ion beam 3 and the supplyof the metal compound 31 are stopped. FIG. 4D illustrates the finalstate in which the just-described step is completed.

Subsequently, as shown in FIG. 4E, the second metal film 6, the firstmetal film 105 and the electrically insulating protective coating 2 arebored through irradiation of the converged ion beam 3. This boring iscontinued until the portion of the metal wire 1 corresponding to theconnecting portion 11 is exposed, that is, until a depth required forelectrical connection is reached. Subsequently, the irradiation of theconverged ion beam 3 is stopped, and the boring of the electricallyinsulating protective coating 2 is completed. FIG. 4F illustrates thestate of the protective coating 2 which is thus bored throughirradiation of the converged ion beam 3.

Subsequently, as shown in FIG. 4G, while the metal compound 31 is beingsupplied, the desired area including the bored portion and a portion ofthe remaining non-bored portion adjacent to the bored portion isirradiated with the converged ion beam 3, thereby forming embedded metalor an electrically conductive film 61 through breakdown of the metalcompound 31 caused by irradiation of the converged ion beam 3. Followingthe formation of the embedded metal 61 having predetermined shape, sizeand thickness which can provide an electrical connection between themetal wire 1 and the second metal film 6, the irradiation of theconverged ion beam 3 and the supply of the metal compound 31 arestopped. FIG. 4H shows the last state in which the just-described stepis completed.

Finally, as shown in FIG. 4I or 4J, the electrical connection betweenthe thus-formed analyzing electrode 4 and the substrate potentialportion 7 is disconnected, and this completes the entire processsequence. As shown in FIG. 3G or 3I, this disconnection is performed insubstantially the same manner as that of the previously-described thirdembodiment. Thus, the detailed description thereof is omitted.

The second metal film 6 and the embedded metal 61 which are obtainedthrough the aforesaid process sequence constitute in combination theanalyzing electrode 4 shown in FIG. 4K.

In the aforesaid fourth embodiment, after the metal wire 1 has beenexposed at the connecting portion 11, the metal compound 31 isdecomposed to form embedded metal 61 through irradiation of theconverged ion beam 3. However, the ion irradiation period in thisembodiment is shorter than the ion irradiation period required in theprevious-described third embodiment. Accordingly, the likelihood ofbreakdown of the semiconductor device 100 is further reduced as comparedwith that of the third embodiment.

It is to be noted that the kind of embedded metal 61 may be the same asor different from that of the second metal film 6.

Also, in either of the respective preferred embodiments described above,in order to form the analyzing electrode 4 on the connecting portion 11,while the metal compound 31 is being supplied to the area including theexposed portion of the metal wire 1, this area is irradiated with theconverged ion beam 3. However, if the metal wire 1 is sufficientlythick, the constituent atoms of the metal wire 1 may be scattered bysputtering to form the analyzing electrode 4 without supplying the metalcompound 31.

In addition, in either of the respective preferred embodiments,reference is made to the formation of a failure analyzing electrode.However, it will be appreciated that the present invention is applicableto the formation of electrodes which are used for other purposes.

Since many changes can be made in the above construction and manyapparently widely different embodiments of this invention can be madewithout departing from the scope thereof, it is intended that all mattercontained in the drawing and specification should be interpretedillustratively and not in a limited sense.

What is claimed is:
 1. A process for forming electrodes forsemiconductor devices having a semiconductor substrate and anelectrically conductive portion covered and protected by an electricallyinsulating coating, said process comprising:a first step of forming anelectrically conductive film on said electrically insulating coating; asecond step of forming an electrode for connection to an externalcircuit on a part of said electrically conductive film, said partcorresponding to a desired position on said electrically conductiveportion; a third step of removing part of said electrode, saidelectrically insulating coating, and said electrically conductive filmto expose the part of said electrically conductive film whichcorresponds to said desired position; a fourth step of electricallyconnecting the remaining part of said electrode and said part of saidelectrically conductive portion which is exposed in said third step byexposing the exposed part of said electrically conductive portion to anion beam; and a fifth step of removing portions of said electricallyconductive film not covered by said electrode.
 2. The process accordingto claim 1, wherein said third step includes irradiating a converged ionbeam onto the portion of said electrically insulating coating at whichsaid electrode is formed to bore a hole through said electricallyconductive film and said electrically insulating coating until saidelectrically conductive portion is reached, thereby exposing a part ofsaid electrically conductive portion.
 3. The process according to claim1, wherein said fourth step involves the formation of an electricallyconductive film between said electrode and said exposed part of saidelectrically conductive portion in providing electrical connectiontherebetween.
 4. The process according to claim 3, wherein said fourthstep includes re-irradiating the vicinity of said hole bored by theconverged ion beam with said converged ion beam while supplying agaseous or vaporized metal compound of the type which is decomposed toproduce metal through irradiation of said converged ion beam, therebyforming said electrically conductive film.
 5. The process according toclaim 1, wherein said electrically conductive film is a planar form ofelectrically conductive film.
 6. The process according to claim 1,wherein said fourth step utilizes erosion in removing the portion ofsaid electrically conductive film which is not covered by saidelectrode.
 7. The process according to claim 6, wherein said erosion iseffected by etching means of the type that erodes said electricallyconductive film but does not corrode said electrode.
 8. The processaccording to claim 7, wherein said etching means is chemical etching. 9.The process according to claim 7, wherein said etching means is plasmaetching employing etching gas.
 10. The process according to claim 9,wherein said etching gas is a mixed gas including carbon tetrafluorideand oxygen.
 11. The process according to claim 3, wherein said metalcompound is tungsten carbonate.
 12. The process according to claim 1,wherein said metal compound is molybdenum carbonate.
 13. The processaccording to claim 1, wherein said electrically insulating coating isselected from the group consisting of a silicon oxide film, a film ofphosphosilicate glass and a silicon nitride film.
 14. The processaccording to claim 1, wherein said electrically conductive film isformed by one of vapor deposition and sputtering.
 15. The processaccording to claim 14, wherein said electrically conductive film is madeof gold.
 16. The process according to claim 1, wherein said electricallyconductive portion is a layer serving as wiring.